@Sid's Trains Nice work! For my $.02 I would have used a larger flywheel, one equal to the diameter of the motor. Stored energy is proportionate to the flywheel diameter AND rpm (which is another good reason to keep the original gearbox!)
I'm late to this party. One important fact that no one thought to mention is that the stall current of a motor is only relevant if it's actually allowed to stall. Rubber tires are a devil's bargain. Scale loco builders don't use them. Instead they weight a loco properly, so that when it's overloaded the wheels are still able to spin. If you measure the motor current under these conditions, it will probably be a lot less than 11 amps! Rubber tires also don't allow the wheels to skid. So when the loco enters a sharp "toy-train" curve, there's a rapid and tremendous increase in friction. These Williams brass locos are more flexible than MTH with their tight wheel gauging and one-piece side rods. But when it happens, stored energy in the flywheel and plenty of motor RPM keep the loco from slowing unnaturally, without requiring some kind of closed-loop speed control. If you don't believe me, turn the speed control "off" and experiment for yourself!
I know that the 42:1 gearbox has more enemies than friends on this Forum, but hopefully there's room for more than one opinion, and mine is that it's not a bad thing. 30:1 or 35:1 might be ideal, but it's ok to err on the high side. I personally have no use for high top speeds; if that's what you want, most of the locos out there run that way out of the box. You did well to keep it. It might allow the motor to slip the wheels even with four of those #$@^#$ tires, hence my comment about measuring max current draw in use. Welcome and look forward to seeing more of your work on the Forum!
